8 classes are annotated with PluginID in Zircon Profile 8

CckMigration in core/modules/migrate_drupal/src/Plugin/migrate/builder/d6/CckMigration.php

Plugin annotation @PluginID("d6_cck_migration");

Messages in core/modules/views/src/Plugin/views/area/Messages.php

Provides an area for messages.

Node in core/modules/node/src/Plugin/migrate/builder/d6/Node.php

Plugin annotation @PluginID("d6_node");

Node in core/modules/node/src/Plugin/migrate/builder/d7/Node.php

Plugin annotation @PluginID("d7_node");

ProfileValues in core/modules/user/src/Plugin/migrate/builder/d6/ProfileValues.php

Plugin annotation @PluginID("d6_profile_values");

Sql in core/modules/migrate/src/Plugin/migrate/id_map/Sql.php

Defines the sql based ID map implementation.

TermNode in core/modules/taxonomy/src/Plugin/migrate/builder/d6/TermNode.php

Plugin annotation @PluginID("d6_term_node");

User in core/modules/user/src/Plugin/migrate/builder/d7/User.php

Plugin annotation @PluginID("d7_user");